Immunoassays have been used in recent years to detect the presence of infectious diseases. In order for the assay to be useful, it must detect a particular organism with a high degree of reliability. In most cases, this requires the isolation and reaction of antigens peculiar to the organism with corresponding antibodies. For the test to be commercially successful, it also needs to be relatively inexpensive, long-keeping, simple to use and rapid.
One such organism which can be detected by immunoassay is Chlamydia trachomatis (herein C. trachomatis) which is one of two microbial species of the genus Chlamydiaceae, order Chlamydiales. There are 15 or more serotypes of this species which are the causes of a number of human ocular and genital diseases including trachoma, inclusion conjunctivitis, lymphogranuloma venereum, nongonococcal urethritis and proctitis. Infection from C. trachomatis is pervasive in the general population so that it is believed that there are millions of cases each year of nongonococcal urethritis alone.
Because of the widespread nature of these diseases, there is considerable interest in having a rapid, simple and reliable test for detection of chlamydial organisms. Assays for C. trachomatis carried out using a solid support are described in U.S. Pat. Nos. 4,497,899 (issued Feb. 5, 1985 to Armstrong et al). The described assays are performed by extracting antigen from the organism and coating it on a bare solid support. The coated antigen is then detected with either one or two antibodies, one of which is suitably labeled. The critical feature of the assays appears to be the use of a solid support for attachment which is untreated or uncoated with any material. Attachment of antigen is apparently achieved by incubating the coated support for an extended time sufficient to cause adsorption of antigen thereon. The entire assay described in U.S. Pat. No. 4,497,899 takes at least 3 hours to perform.
A much more rapid test for chlamydial organisms which has high reliability and can be performed at room temperature is described and claimed in U.S. Ser. No. 255,923 (filed on Oct. 7, 1988 by Pronovost). Our colleague found that ionically charged (specifically cationic) supports attract chlamydial antigen and enable one to quickly and sensitively detect the antigen.
A further improvement is described in U.S. Ser. No. 255,920 (filed Oct. 7, 1988 by Mauck) which describes the use of a surfactant-coated uncharged membrane in chlamydial assays. That invention enables one to rapidly and sensitively detect the antigen in biological specimens that contain copious amounts of whole blood, mucus or components thereof.
A large portion of the market for chlamydial assays is intended for doctors' offices where there is limited capacity for refrigeration of test kits. Thus, while the inventions described above provide important advances in the art, there is a further need to have reagents and test kits which can be stored for long periods of time without refrigeration before use while maintaining sensitivity and low background in the assay.
The current product marketed by Kodak as the Surecell.TM. Chlamydia Test Kit has been received by the marketplace quite positively. It utilizes a disposable test device containing a surfactant-coated Biodyne.TM. polyamide membrane like that described in the Mauck application noted above. It is highly desirable to increase the storage keeping of the reagents in that kit, and to keep the background in the assay low. This needs to be accomplished without the need for extensive refrigeration.